How could wrong Amperage affect a laptop

[Undeadlord]

Guys and gals,

I have recently been seeing some of my more "technical savvy" users, using power supplies for their laptops that are power supplies from diffferent models.

For example, most users have Compaq M700's and it takes a power brick that puts out 18.5V and 2.7A .. some people however are using the new Compaq EVO's and their power brick puts out 18.5V but 3.5A. I have seen people using these EVO power bricks to run their M700's which means the M700 is getting almost an whole amp more than it should. I know nothing about electrical work beyond a few basics. What kinds of problems could this cause .. if any? Thanks!

Undeadlord

[westly197]

Typically electronics will only draw the current they need, so extra is ok. (This applies to amps not volts) Think of the power supply in your desktop PC, do you have to have one that is just enough or do you like to use one with more then is needed? Say 300-400 Watt when a basic system would likely run on 150watts. (P.S. watts is a function of amps and volts, since the voltage output is the same, it's the amps that increase when you get a higher watt power supply)

[MaxVal]

The important thing is having the correct voltage with sufficient amperage available.
Think of electricity in terms of water... pressure being equivalent to voltage, and flow rate equivalent to amps.
Having the correct pressure with sufficient flow is critical. If more flow is available, it will remain unused and effect nothing.
Additional pressure (volts) would cause additional flow (more amps), not good!
If the device wants more flow (amps) than is available, pressure drops (voltage).
Hope this helped more than hurt...
MAX

[John Prophet]

It shouldnt cause any because the rating of a power supply is only what its CAPABLE of GIVING.

So if its CAPABLE of giving 3.5 amps, but the laptop only USES 2.5 or so..then the power supply will only give 2.5.

You can look at amperage as a well to draw from..it will only give what the laptops asks for.....amperage is not like a rushing river that overruns the banks etc.


Quote "I have seen people using these EVO power bricks to run their M700's which means the M700 is getting almost an whole amp more than it should." The key word here is "getting"....its NOT "getting" more than it should..it still only "gets" what it needs...its just that the 3.5amp supply could "GIVE" more if its needed to...but it wont give more than the laptop asks for.

Actually the only benefit to the lower rated model is cost.

If anything the higher rated power supply will obviously be better because it will be more stable since it is only "cruising" with the laptop.


Here's another comparison...when you plug a TV into a wall socket at your house..the TV is probably going to draw 1 Amp maximum...but the wall socket can give about 15 amps!! So its not a matter of the TV "getting" more than it should...it only gets what it needs.

Hope I didnt confuse you worse! lol...JP

[Undeadlord]

MaxVal, I remeber my teacher in highschool explaining Voltage and Amps in that same way

Thanks guys, I am just glad to know that I would be having laptops blowing up or anything. Thanks again!

Undeadlord

[John Prophet]

Now, going the other way and using an UNDERamped supply would be like when you take a shower and someone flushes the toilet! The pressure (voltage) would sag.

having the extra current potential is good because sometimes you could have a high current needed for just an instant (peak). If you have a 2.7 supply and the laptop asks for 2.6 the 2.7 could "sag" just for an instant, causing a blue screen or other problem....but the 3.5 wouldnt even really notice..it would keep all of its outpot voltages solid.

JP

[Choub890]

Hey guys, i am new here and i have a question related to this topic. I am looking at an external battery for my laptop. Here is some info on the battery and the laptop AC Adapter:

AC Adapter output: 24V/1.5A
External Battery output: 19V/3.75A

I would like to know if the battery would work on my laptop. I know that the voltage is lower (19V VS 24V), but it also gives out more amps (3.75A VS 1.5A). Now I am reassured that the laptop will only take the amp it needs and not more (so that rules out that the laptop will blow up if ever i plug it in XD), but now i'd like to know if the battery would be ok for my laptop (if it would power on and have no problem).

Thanks for your time.

[shizzzon]

it doesnt' matter!

You are trying to compare total watts and that has NOTHING to do with it.

I have been into car audio competition and designs for people for a while so i have to know this or else i might as well not even try...

It is possible to use different DC voltage +\- it's rating but you are doing a guessing game and a bad one at that!

Lower voltage makes things work slower and generates more heat.
Higher voltage makes things work faster which also generates more heat.

The point is both examples will cause premature failure either immediately or over time...

Like in a car - the voltage coming off your alternator must be about 110% minimum that of the float voltage of your battery for it to properly charge the battery.

If the voltage is not that much higher than the battery's float, then it will only charge so much of the battery. I don't care how many amps the alt can disperse to the battery, it just couldnt top it off as much as if the voltage were higher.

Voltage is THE most important part in terms of properly running electronics. Amps cannot directly damage a product because you either have enough or you don't.

Typically, if you do not have enough amps, the device will never operate.
Now, if you just had JUST ENOUGH, it can either make a device work slower than normal or prematurely kill it because it's beggin for power.

[Choub890]

it doesnt' matter!

You are trying to compare total watts and that has NOTHING to do with it.

I have been into car audio competition and designs for people for a while so i have to know this or else i might as well not even try...

It is possible to use different DC voltage +\- it's rating but you are doing a guessing game and a bad one at that!

Lower voltage makes things work slower and generates more heat.
Higher voltage makes things work faster which also generates more heat.

The point is both examples will cause premature failure either immediately or over time...

Like in a car - the voltage coming off your alternator must be about 110% minimum that of the float voltage of your battery for it to properly charge the battery.

If the voltage is not that much higher than the battery's float, then it will only charge so much of the battery. I don't care how many amps the alt can disperse to the battery, it just couldnt top it off as much as if the voltage were higher.

Voltage is THE most important part in terms of properly running electronics. Amps cannot directly damage a product because you either have enough or you don't.

Typically, if you do not have enough amps, the device will never operate.
Now, if you just had JUST ENOUGH, it can either make a device work slower than normal or prematurely kill it because it's beggin for power.

Is overheating the only thing that will kill my laptop? If so, then is it safe to assume that if my components are not overheating when i plug in the battery (i can monitor the temperatures of the various pieces of hardware), then my laptop will be fine?

Thanks for your reply.

[Flying JJ]

Hey guys, i am new here and i have a question related to this topic. I am looking at an external battery for my laptop. Here is some info on the battery and the laptop AC Adapter:

AC Adapter output: 24V/1.5A
External Battery output: 19V/3.75A

I would like to know if the battery would work on my laptop. I know that the voltage is lower (19V VS 24V), but it also gives out more amps (3.75A VS 1.5A). Now I am reassured that the laptop will only take the amp it needs and not more (so that rules out that the laptop will blow up if ever i plug it in XD), but now i'd like to know if the battery would be ok for my laptop (if it would power on and have no problem).

Thanks for your time.

Well, just don't use that battery. The lower voltage will cause a higher current draw. The insulation ( dielectric ) will break down on the components in your system due to the heat from the current it will now draw. When they break down sufficiently, current will flow through the "short circuits" either to ground or potentially another component. You will then let have a dead system. Having the higher amperage rating will only let more current flow at the reduced voltage and potentially mask the problem until failure occurs.

it doesnt' matter!

You are trying to compare total watts and that has NOTHING to do with it.

I have been into car audio competition and designs for people for a while so i have to know this or else i might as well not even try...

It is possible to use different DC voltage +\- it's rating but you are doing a guessing game and a bad one at that!

Lower voltage makes things work slower and generates more heat.
Higher voltage makes things work faster which also generates more heat.

The point is both examples will cause premature failure either immediately or over time...

Like in a car - the voltage coming off your alternator must be about 110% minimum that of the float voltage of your battery for it to properly charge the battery.

If the voltage is not that much higher than the battery's float, then it will only charge so much of the battery. I don't care how many amps the alt can disperse to the battery, it just couldnt top it off as much as if the voltage were higher.

Voltage is THE most important part in terms of properly running electronics. Amps cannot directly damage a product because you either have enough or you don't.

Typically, if you do not have enough amps, the device will never operate.
Now, if you just had JUST ENOUGH, it can either make a device work slower than normal or prematurely kill it because it's beggin for power.

You are trying to compare total watts and that has NOTHING to do with it.
Not entirely correct. Wattage is the basis of every electrical calculation there is. We have standard voltages and the currents of diffrent "appliances" ( this case computers ) differ. The manufacturer determines how much power ( watts ) an appliance will use. They then determine what voltage is the most feasable to use. A higher powered ( again watts ) unit will be better run with a higher voltage and less current ( causes heat ). Think air conditioners here, the big ones are 240 VAC vs. the smaller 120 VAC units. Plug either into the wrong voltage and see what happens. Computers being less power hungry are usually 120 VAC rectified to a nominal 12 VDC. They then take the 12 VDC and lower it even more for their uses like the cpu at +/- 1.2 VDC ( how would you insulate the chip internally for a higher voltage ). The manufacturer will figure this out but with much less voltage and current ( power = voltage x current )from the power supply. You must look at the total wattage, but the voltage is also very critical as you state below. Most look first at the voltage and then ensure that there is enough current. When you do this ( voltage and current ) you are in fact looking at the power. An overly big power supply is dangerous in that it can supply more power than your appliance can handle. Even if the voltage is correct. Why do you think we have small breakers for branch circuits in our houses?

Voltage is THE most important part in terms of properly running electronics. True but there is a balance between the two. Amps cannot directly damage a product because you either have enough or you don't. True if you assume a correct voltage and power draw, but if these 2 are correct, the amperage would also fall in line ( Ohm's law derivation ). Amps are what will do the damage voltage will just allow the amps to flow easier. An undervolted system will draw more amps causing heat and insulation degredation. This will allow even the lower voltage to gap across. A little leakage current will only cause more heat and the death spiral of more insulation breakdown, more current untill poof your done. An over voltaged system may not have the dielectric strength to withstand the higher voltage and the above will happen quicker ( sometime instant ) or, if it can withstand the potential ( voltage ) it will draw less current and not work and will eventually fail due to trying to run on the reduced current.

Typically, if you do not have enough amps, the device will never operate.You will kill the power supply. Or you may have a voltage droop as it tries to compensate and the rectifier is overwhelmed. The diode bridge will fail and you may pass the AC directly to the powered component.
Now, if you just had JUST ENOUGH, it can either make a device work slower than normal or prematurely kill it because it's beggin for power. True but don't forget surges. You will probably kill one or both over the long run.

Sorry if this seems like a ramble, I'm tired have been running a power plant all day. For 19 years before that I was a nuclear and industrial electrician. I have seen the results of over and under voltage on many things, some very expensive.

[Choub890]

Ok so... Behind my laptop it says (just saw this): DC rating: 19V/4.74A. I am confused as to what i should consider to be the true DC rating... My AC Adapter says 24V/1.5A, my battery 10,8V and now this new reading. Which one is it?

[michealjackson]

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[jackthaboi]

I used a power supply on my dell inspiron 1300 that was a 1.5 amps less than the oem one. It ran my computer fine, but now it won't detect my battery and just says that it isn't installed. Too many amps is OK, but not enough might screw something up. Unfortunately I learned the hard way.

[saint2300]

My laptop original DC adapter is rated as 19V 3.5A,
can I use 20V 5.0A adapter on it? Will it cause harm to the system?

[josborn]

For all those who claim that your laptop will draw only the power it needs, stop and think! Look at the power cord for a laptop vs. the power cord for your desktop. Notice that big box on the laptop cord? Yes, it is true that the devices are designed to draw only the power that they need, but when you change power cords, you are changing the device! Unlike your desktop, where the power supply management is built inside the box, a laptop has the power management supply built into the cord. Changing the power supply cord on your laptop is like changing the power supply box inside your desktop, you need the right power supply for your machine. Look at the input and output ratings on the cord. What comes out of the cord is what is being fed into your laptop. The wrong power supply WILL damage your laptop. Your laptop will most likely run fine for a while. but continued use of the wrong power supply WILL FRY your machine. It may take a few weeks or a few months depending on how off the power supply you are using is from the manufacturer's specs. The components in your laptop do not manage how much power is being sent to it, look at the motherboard, look at the chip, there is nothing there to manage the power coming in. What controls the power going into your laptop and it's sensitive components is that box on your power supply cord. That's why it is there!!! Do yourself a favor, just because the plug fits, doesn't mean it's the right power supply, read the specs and make sure it matches!

You can put 87 octane gas in your Vette, but will it run as well as 93 octane? What happens to your 2-stroke engine if you don't have the right gas/oil mixture? The engine either runs rough or it burns up.

[josborn]

Typically electronics will only draw the current they need, so extra is ok. (This applies to amps not volts) Think of the power supply in your desktop PC, do you have to have one that is just enough or do you like to use one with more then is needed? Say 300-400 Watt when a basic system would likely run on 150watts. (P.S. watts is a function of amps and volts, since the voltage output is the same, it's the amps that increase when you get a higher watt power supply)

WRONG!!! THE POWER SUPPLY CORD IS WHAT DRAWS THE POWER! WHEN YOU CHANGE THE POWER SUPPLY CORD TO SOMETHING DIFFERENT FROM WHAT THE MANUFACTURER RECOMMENDS, YOU ARE CHANGING THE POWER GOING INTO YOUR LAPTOP. THAT'S WHAT THE BOX ON YOUR POWER CORD IS FOR!!! THAT'S WHY THERE IS A FUSE INSIDE THE BOX ON YOUR POWER CORD. IF THE SPECS ON THE POWER CORD DO NOT MATCH THE MANUFACTURER'S SPECS, THEN YOU ARE VOIDING ANY WARRANTY YOU HAVE ON YOUR LAPTOP AND YOU ARE GOING TO TRASH IT. IT MAY NOT FAIL FOR A FEW WEEKS OR A FEW MONTHS, DEPENDING ON HOW OFF THE SPECS ARE, BUT YOU WILL TRASH YOUR LAPTOP. WHY TAKE THE CHANCE??? YOU CAN BUY A REPLACEMENT ON EBAY, AMAZON, OR EVEN CRAIGSLIST, USUALLY FOR UNDER $20. IS IT WORTH TRASHING A LAPTOP YOU SPENT HUNDREDS OR OVER A $1000 ON TO SAVE $20?

[evereddie]

Josborn, while you are trying to help you really don't know what you are talking about. Using the term "POWER" shows that. It really comes down to volts and amps. Volts HAS to be the same as what original specs are called for, more amps will not hurt anything. It is a fact that the device will draw only the amps that it needs. PERIOD.
Read up a little. Education is a good thing.

[howste]

For all those who claim that your laptop will draw only the power it needs, stop and think! Look at the power cord for a laptop vs. the power cord for your desktop. Notice that big box on the laptop cord? Yes, it is true that the devices are designed to draw only the power that they need, but when you change power cords, you are changing the device! Unlike your desktop, where the power supply management is built inside the box, a laptop has the power management supply built into the cord. Changing the power supply cord on your laptop is like changing the power supply box inside your desktop, you need the right power supply for your machine. Look at the input and output ratings on the cord. What comes out of the cord is what is being fed into your laptop. The wrong power supply WILL damage your laptop. Your laptop will most likely run fine for a while. but continued use of the wrong power supply WILL FRY your machine. It may take a few weeks or a few months depending on how off the power supply you are using is from the manufacturer's specs. The components in your laptop do not manage how much power is being sent to it, look at the motherboard, look at the chip, there is nothing there to manage the power coming in. What controls the power going into your laptop and it's sensitive components is that box on your power supply cord. That's why it is there!!! Do yourself a favor, just because the plug fits, doesn't mean it's the right power supply, read the specs and make sure it matches!

The "box" you so eloquently described is a power inverter. It changes AC current from the power outlet into DC current at a given voltage. For most power supplies, there are only two wires which provide electricity. As was explained 8 years ago in this thread, this is supplied at a given voltage (constant) and a maximum current (variable upon demand). If the voltage is wrong, there could be damage. If the amperage is too low, it may cause problems as well.

While your advice is generally good (don't just plug it in because it fits) an informed user can actually use a power supply that wasn't designed for a specific model if the specs are adequate.

You can put 87 octane gas in your Vette, but will it run as well as 93 octane? What happens to your 2-stroke engine if you don't have the right gas/oil mixture? The engine either runs rough or it burns up.

Thes are two great examples of what's known as "false analogy fallacy." Thanks for the amusing comparisons.

[ToshibaL305D]

My laptop requires 19V/4.74A and I needed a 3-prong adapter because the default one had only 2. I researched the right replacement part for that adapter and found an adapter with the same code on Amazon. The new adapter I bought was giving the following output: 19V/6.5A.
My laptop died yesterday after 11 days of using the new adapter. Been using my laptop for 2 years before that. The last posts here are contradicting each other. I am not sure what happened... but it will cost me a lot more to repair it. Does anyone have an explanation for this?

[stroyal]

My laptop requires 19V/4.74A and I needed a 3-prong adapter because the default one had only 2. I researched the right replacement part for that adapter and found an adapter with the same code on Amazon. The new adapter I bought was giving the following output: 19V/6.5A.
My laptop died yesterday after 11 days of using the new adapter. Been using my laptop for 2 years before that. The last posts here are contradicting each other. I am not sure what happened... but it will cost me a lot more to repair it. Does anyone have an explanation for this?

If the laptop draws 4.7, it will only draw 4.7, no mater what the adapter is capable of. The voltage is critical though.

That is the nature of any electrical device.

For example a 15amp circuit, with a computer plugged in won't draw 15amps, it only draws what the computer requires, 4, 6, 8 amps, depending on the Wattage.

Another example, a 100 watt light bulb draws .83 amps @ 120volts, when plugged into a 15amp circuit.


The trouble happens the other way.

A 20amp device, plugged into a 15 amp circuit, WILL draw 20amps, and lift the breaker, if there is one. If not, it will draw 20amps, until something burns up.

It is the device that governs, the draw.

It must be another problem.
I'd check the voltage of the adapter, with a multi-meter.
Edit
Of course to really test it, you would have to have it under load.

Things must be different on Josborn's planet.

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